Integrated air inlet system for multi-propulsion aircraft engines

ABSTRACT

An air inlet duct for an air-breathing combined-cycle aircraft engines is internally divided into separate channels for low-speed and high-speed components of the engine, and contains one or more movable panels that are fully contained within the duct and pivotal between an open position in which incoming air is directed to both channels and a closed position in which all incoming air is directed to the channel leading to the high-speed engine. This integrated duct utilizes all incoming air at all stages of flight with no change in either the geometry of the air capture portion of the engine or the engine itself, and no exposure of movable leading edges. The result is a minimum of shock waves and a high degree of efficiency in operation of the engine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention resides in the field of air-breathing engines, andparticularly combination engines that incorporate both a ramjetcomponent and a low-speed booster component such as a rocket or aturbojet.

2. Description of the Prior Art

Air-breathing engines for hypersonic applications are known as “combinedcycle” systems because they use a graduating series of propulsionsystems in flight to reach an optimum travel speed or to leave theatmosphere altogether. Air-breathing engines use atmospheric air as asource of oxygen for combustion, as opposed to rockets which carry theirown oxidizer. By using air captured from the atmosphere, air-breathingsystems are several times more efficient than conventional rockets.

The thrust upon takeoff of a combined cycle engine and operation of theengine at low-to-moderate Mach numbers is achieved by a booster unitwhich consists of either rockets or turbojets or a combination of thetwo. Once the vehicle has reached a speed of Mach 2 or greater, thebooster unit is replaced by a ramjet (which term is used genericallyherein to include “scramjet”) and acceleration is continued. Thebooster-to-ramjet transition is a critical stage in the operation of theengine since any loss of air flow through either engine during thetransition can result in a loss of compression efficiency. The need toshift inlet air from the booster propulsion system to the high-speedpropulsion system has resulted in large geometries that create flowresistance, surfaces and leading edges that produce complex shock waves,areas of separated or recirculating flow, and exposed moving parts thatare vulnerable to damage.

SUMMARY OF THE INVENTION

It has now been discovered that a combined cycle engine can be designedwith an integrated air duct that receives atmospheric air at an entryregion of unchanging dimensions and directs all of the incoming air tooperating components of the engine during all stages of acceleration,including the low-speed (booster), transition, and high-speed stages.The air enters through an air inlet that has fixed (i.e., immovable)external walls. A fixed internal wall within the integrated duct dividesthe interior of the duct into two channels—one leading to the high-speedengine and the other to the low-speed engine. The fixed internal wallhas a leading rim commencing either downstream of or at the downstreamend of, the capture tube. The channel leading to the high-speedpropulsion system thus begins at this location. A movable panel orseries of movable panels within the integrated duct moves between anopen position and a closed position and all positions in between, theopen position allowing incoming air to enter both the low-speed and highspeed channels, and the closed position directing all of the incomingair flow to the high-speed channel. In preferred configurations, thelow-speed channel is a peripheral channel, i.e., one that is positionedbetween the high-speed channel and the external walls of the integratedduct, fully surrounding the high-speed channel. In certainconfigurations within the scope of this invention, however, thehigh-speed channel is not coaxial with the integrated duct and thelow-speed channel extends only partially around the high-speed channel.In certain embodiments as well, the width of the peripheral channel(leading to the low-speed engine) varies along the circumference of thehigh-speed channel. In these embodiments, the movable panels areconstructed and arranged around the high-speed channel accordingly. Inall embodiments, the movable panels are operated during takeoff andacceleration to initially direct all entering air to both the low-speedengine and the high-speed engine and then, after a transition stageduring which the proportion of air entering the channel leading to thelow-speed engine is gradually reduced, directing all entering air to thehigh-speed engine.

This invention therefore resides in integrated air ducts forcombined-cycle engines and in combined-cycle engines themselves thatincorporate these integrated air ducts. In the combined-cycle engines,the low-speed component is either one or more turbojets, one or morerockets, or a combination of rockets and turbojets. Such a combinationallows the use of a smaller turbine engine(s) without sacrificingcritical thrust during the takeoff and transition stages. One advantageof the integrated air ducts of this invention and the engines in whichthey are used relative to the prior art is that all incoming air isutilized during all stages of takeoff and acceleration, thereby allowingthe use of a larger volume of atmospheric air for combustion at anysingle stage. This also reduces the weight and volume of the engine as awhole. Another advantage of the engines of this invention is that thearrangement of internal channels and movable panels allows air to enterthe high-speed channel while the vehicle is still traveling at arelatively low Mach number, and the movement of the panels provides asmooth transition between the stages. A third advantage is that themovable panels can be constructed without leading edges that are exposedto the high enthalpy air flow. This permits the panels and the engine asa whole to be of more durable construction and to reduce the generationof shock waves that prevent air from entering the engine. The ability toallow air to enter the high-speed engine while the low-speed engine isstill operating, the higher mass capture of atmospheric air, theimproved pressure recovery, and the reduction in drag caused by thespill of atmospheric air at all speeds collectively result in an enginewith a thrust and a specific impulse (I_(sp)) that are significantlyhigher than those of many combined-cycle systems of the prior art.

These and other features, embodiments, and advantages of the inventionwill be apparent from the description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an aircraft vehicle incorporatingengines and air inlet systems in accordance with the present invention.

FIG. 2 is a bottom view of one of the air inlet systems and associatedengines of the vehicle of FIG. 1.

FIG. 3 is a longitudinal cross section of the air inlet system of FIG.2.

FIG. 4 is a rear view of the air inlet system of FIG. 3 taken along theline 4-4 of FIG. 3.

FIG. 5 is a longitudinal cross section of a second air inlet andcombined-cycle engine system within the scope of the present invention.

FIG. 6 is a rear view of the air inlet and engine system of FIG. 5.

FIGS. 7A and 7B are front views of alternative examples of injectorsmounted to the inside wall of the channel leading to the high-speedcomponent of the system of FIGS. 5 and 6.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

While this invention covers a wide range of configurations, geometries,and applications, an understanding of the features that are common toall embodiments and that define the invention and its operation as awhole can be obtained by a review of specific examples. The drawingsaccompanying this specification and their description below relate toseveral such examples; others will be readily apparent to those skilledin the art.

A front view of a vehicle containing engines and integrated air ducts inaccordance with the present invention is shown in FIG. 1. The vehiclecontains two combined-cycle engines with a separate air inlet 11, 12 foreach. Inside each of the air inlets are throats of circular crosssection that lead to the ramjet engine components. The air inlets 11, 12are not vertically centered in the vehicle body but instead offsettoward the bottom of the vehicle. The opening 16 of each inlet followsthe aerodynamically shaped contour of the vehicle, and the shape of theopening can be seen most clearly in the bottom view shown in FIG. 2. Asshown in this bottom view, the upper lip 17 of the air inlet extendsforward of the remainder of the inlet. The air inlet is thus open at thebottom for much of its length. This opening allows spillage of air fromthe capture tube to the exterior of the aircraft in response to theshock waves that are generated inside the capture tube duringacceleration from low-speed flight. This spillage regulates the airpassing into the inlet.

Of the air entering the inlet 12, the portion that remains within theduct past the downstream end 20 of the opening at the bottom of theinlet remains within the engine, entering the internal channels andfeeding whichever engine components are in operation at any given stageof vehicle flight. The engine components themselves are shown inschematic. Of these, the booster engine 21, which in the embodiment ofFIG. 2 is a turbine engine, is positioned to one side of the air inlet12 and receives combustion air from a channel 22 that originates withinthe air inlet at the periphery of the inlet. The channel 22 ispreferably of variable cross section to decelerate the air as necessaryto reach subsonic flow. The ramjet or high-speed engine 23 is co-linearwith the air inlet from the perspective shown in the drawing, andincludes fuel injectors 24, a throat 25, a combustor 26, and a divergingportion 27 to form a supersonic nozzle.

The air inlet 12 and the ramjet components are generally aligned along alongitudinal axis 28 which is approximately parallel to the direction offlight and, with the moving vehicle as a frame of reference, parallel tothe direction of the approach of atmospheric air. Cross sectionsreferred to herein as “longitudinal” are those that are taken in planesin which this longitudinal axis resides, while cross sections referredto as “transverse” are those taken in planes that are perpendicular tothis axis.

FIG. 3 is a vertical longitudinal cross section of the integrated airinlet of FIG. 2, showing the interior of the integrated air duct and thelow-speed and high-speed air channels. The upper lip 17 of the airinlet, as noted above, extends forward of the remainder of the inlet,and the opening along the bottom portion of the inlet tapers to aclosure 20 (the taper is shown in FIG. 2). All air remaining within theinlet downstream of this closure 20 is fully available for use by theengines. An internal wall 32 divides the region downstream of theclosure point 20 into two channels—a ramjet (high-speed) channel 34 anda booster engine (low-speed) channel 35. In preferred embodiments of theinvention, the ramjet channel is of circular cross section and itsleading rim 33 is downstream of the tapered closure 20 of the opening atthe bottom of the external wall. A turbine engine 36 is shown in thebooster engine channel.

The ramjet channel 34 remains open at all times to receive air from theinlet. The booster engine channel 35 is either open or closed dependingon the position of the movable panel 37 at the forward end of thebooster engine channel. The panel 37 is movable between an open positionshown in solid lines and a closed position shown in dashed lines. Whenthe panel is in its open position, all incoming air is divided betweenthe ramjet channel 34 and the booster engine channel 35. When the panelis in its closed position, all incoming air is directed to the ramjetchannel 34. Thus, there is no change in the total flow rate of incomingair that is used for combustion in the combined-cycle engine as theoperation of the engine shifts from a booster stage to the ramjet stage;air from the entire transverse cross section of the air inlet is used atall times. Air is thus allowed to enter the ramjet while the boosterengine is still in use and a maximum quantity of air is used at alltimes.

Movement of the panel 37 between the open and closed positions isachieved by pivoting the panel around a hinge or pivot axis 38, which inthis embodiment is approximately co-planar with or slightly forward ofthe location of the closure point 20 in the bottom of the outer wall ofthe air inlet. As the panel moves toward its closed position, the use ofthe booster engine is gradually diminished until all air is fed to theramjet engine. In preferred embodiments of the invention, the positionof the panel provides each internal channel with a shape that serves theneeds of the engine fed by that channel. Thus, for example, when theinlet air is subsonic relative to the vehicle, the desired panelposition is one that causes the channel to diverge to form an expandingcross section and when the inlet air is supersonic, the desired panelposition is one that causes the channel to converge to form a narrowingcross section before diverging downstream. In the embodiment shown inFIG. 3, the booster engine is a turbine engine which operates withsubsonic inflow. Accordingly, when the movable panel 37 is in its openposition, the panel is angled away from the axis 27 and the channel wallformed by the panel diverges. Likewise, when the movable panel is in theclosed position, the panel is angled toward the axis 27 and the paneland the forward portion 17 of the capture tube form a continuous wallthat provides the channel with a converging cross section. The length ofthe movable panel in this embodiment is equal to the distance betweenthe pivot axis 38 and the leading rim 33 of the ramjet channel wall 32.All inlet air thus converges toward the throat which is formed by theramjet channel wall 32.

As an optional feature, further control of the air speed through thebooster channel 35 is achieved by the inclusion of a second movablepanel 39 downstream of the first movable panel and pivotally mounted tothe external wall of the air inlet at a separate pivot axis 40. Like theforward panel 37, this aft panel 39 can be adjusted to any angle betweentwo positions, one shown in solid lines and the other in dashed lines.When the approaching air speed (relative to the vehicle) is supersonicand the turbine engine 36 shown in the booster channel is operating, theair must be decelerated to subsonic speed before it is fed to theturbine compressor. This can be achieved by placing the forward panel 37and aft panel 39 in an intermediate position that would allow air toenter the booster channel and yet provide the channel with aconverging/diverging geometry as is common in aircraft such as the F-14and F-15 supersonic engines. Air entering at supersonic speed is firstdecelerated in the converging section of this converging/diverginggeometry to sonic or near sonic speed and then decelerated further inthe diverging section.

In view of their functions, the forward and aft panels can be termed a“flow-diverting panel” and a “diffuser panel,” respectively. Theflow-diverting and diffuser panels can be joined or can meet at theirmovable ends, but in some cases it is preferable to leave a small gapbetween them to manage the inlet boundary layer by removing low energyair from the inlet tract. In embodiments that include the diffuser panelas well as those that include only the flow-diverting panel, all movingparts are contained within the interior of the integrated air duct.

While only one booster engine channel 35 is shown in FIG. 3, two or morebooster engine channels are preferably included and arranged around thecircumference of the ramjet engine channel 34, since in preferredembodiments of this invention the ramjet channel will be approximatelycircular in cross section and occupy less than half of the crosssectional area of the engine. There may for example be three boosterengine channels, as visible in the view shown in FIG. 4, which is a rearview facing the outlets of the channels. These channels include an upperchannel 51, and two side channels 52, 53, with no bottom channel sincethe ramjet channel is positioned at the bottom of the vehicle. Otherconfigurations within the scope of this invention will have a differentnumber of booster channels that will either partially or completelyencircle the ramjet channel, depending on the dimensions and geometriesof the channels. A flow-diverting panel will be positioned within eachbooster engine channel, and when diffuser panels 39 are included, onewill likewise be included within each booster engine channel.

In this embodiment of the invention, each booster channel is shaped as ashroud 54, extending radially outward from the ramjet channel 34 andforming a cavity within which the flow-diverting and diffuser panels canbe raised to their open positions and lowered to their closed positions.In the view shown in FIG. 4, the panels occupy an intermediate positionbetween fully open and fully closed, and only the diffuser 39 and therear edge 55 of the flow-diverting panel are visible. The movement ofthe panels is indicated by the arrows 56 that show the movement of therear edge 55 of the flow-diverting panel. In the fully closed position,this rear edge 55 is lowered to meet the wall of the ramjet channel 34.

FIGS. 5 and 6 depict a rocket-based combined-cycle engine which is avariation on the configuration shown in FIGS. 1 through 4. Thehigh-speed engine in this rocket-based combined-cycle engine is ascramjet combustor, the booster engines are ramjet combustors fed byair-augmented rockets rather than turbojets, and the low-speed channel61 that supplies air to the ramjet combustors is annular, completelyencircling the channel 62 to the high-speed (scramjet) engine. Thearrangement of the booster engines around the scramjet engine islikewise generally symmetrical, and the movable panels are likewisesymmetrically arranged around the scramjet engine channel. FIG. 5 is across section of the engine, showing the various channels and onemovable panel 63 for purposes of illustration. As in FIG. 3, the openposition of the movable panel 63 is represented by solid lines and theclosed position by dashed lines. When closed, the downstream end of themovable panel abuts the leading edge of the internal wall 64 thatdefines the scramjet engine channel.

In this particular embodiment, a second set of movable panels,represented in FIG. 5 by a single panel 65, is positioned at thedownstream end of the ramjet combustor. Like the forward panels 63,these aft panels 65 have an open position, shown in solid lines, and aclosed position, shown in dashed lines. The movement of these aft panels65 between these two positions is coordinated with the movement of theforward panels 63 to fully open the ramjet combustor passages duringlow-speed operation and to fully close them at both the upstream anddownstream ends during high-speed operation when the scramjet is fullyoperational, avoiding recirculation bubbles and dead volumes.

Movement of the forward and aft panels 63, 65 in the embodiment shown inFIG. 5 as well as those in the embodiment of FIGS. 3 and 4 and allembodiments of the invention is achieved by conventional means wellknown to those knowledgeable in the design and manufacture of aircraftvehicles. Actuators 66, 67 (FIG. 5) can be included in the vehicleitself to move the panels and control their position. Actuators of knowndesign such as hydraulic actuators, pneumatic actuators, orelectromagnetic actuators can be used, including linear motors, linearscrews, solenoids, SC PM motors, stepper motors, induction motors, andothers that will readily occur to the skilled engineer.

FIG. 6 is a rear view of the combined-cycle engine of FIG. 5. Theexternal wall 71 of the engine and the high-speed (scramjet) enginechannel 72 are both of substantially circular cross section and coaxial.The expanding section 73 of the external wall downstream of both thelow-speed and high-speed combustors serves as the diverging section ofboth the low-speed and high-speed components of the engine. The tubularwall 74 of the air-supply channel to the high-speed engine is supportedby a series of radial struts 75. The movable panels are positioned inthe regions between the struts, and in this rear view the movable panelsthat are visible are the downstream panels 76. A rocket 77 is mountedwithin each strut to assist in startup of the engine and also to serveas fuel injectors to feed the ram combustor. These rocket/injectors 77are contained within the low-speed channel 61 and their discharge islikewise retained in this channel.

A series of injector pylons 78 extend into the high-speed channel 62.These injector pylons are symmetrically arranged around the periphery ofthe high-speed channel and inject fuel for operation of the scramjet.Rockets can also be placed within these injectors for firing to providethe engine with further thrust during boost and also when the engine isoperating at very high speeds. Alternate shapes of the injector pylons78 are shown in the front views of FIGS. 7A and 7B. The injector pylon78a of FIG. 7A is a low drag design with a forward surface 79 thattapers toward the front to a point 80 on the channel wall. The forwardsurface of the injector pylon 78b of FIG. 7B is a broad ramp 81,producing a faster mixing of fuel and air.

In a still further variation, turbine engines, rockets, and a scramjetengine can be combined to form a turbine-and-rocket-based combined-cycleengine. In this variation, turbine engines serve as the booster enginesreceiving their combustion air through a peripheral channel as shown inFIGS. 1 through 4, or in a symmetrical arrangement uniformly distributedaround the entire circumference of the high-speed channel, and rocketsfor additional thrust during boost and at very high speeds arepositioned within mounts such as the injector pylons 78 shown in FIGS. 5and 6.

The foregoing is offered primarily for purposes of illustration. Furthervariations and modifications that utilize the same novel features ofthis invention and therefore also fall within the scope of thisinvention will readily occur to the skilled aircraft engineer.

1. An integrated air duct for an aircraft engine with multiplepropulsion systems, said integrated air duct comprising: a fixed outerwall with an opening for incoming air, wherein said opening has aforward-extending upper lip and a rearward-extending downstream end, afixed inner wall dividing said duct into a first channel having aleading rim downstream of said opening and a second channel between saidfixed inner wall and said fixed outer wall, a movable panel mountedwithin said fixed outer wall at a pivot axis downstream of said upperlip and approximately coplanar with or slightly forward of saiddownstream end, said pivot axis also being upstream of said leading rimof said first channel for pivoting between an open position allowingincoming air entering through said opening to enter said first andsecond channels simultaneously and a closed position obstructing airentry into said second channel and thereby causing substantially allincoming air entering through said opening to enter said first channel,and means for moving said movable panel between said open position andsaid closed position.
 2. The integrated air duct of claim 1 wherein saidmovable panel when in said closed position extends from said pivot axisto said leading rim of said first channel.
 3. The integrated air duct ofclaim 1 wherein said movable panel when in said closed position forms aconverging flow passage from said pivot axis to said leading rim of saidfirst channel.
 4. The integrated air duct of claim 1 wherein saidmovable panel when in said closed position forms a converging flowpassage from said pivot axis to said leading rim of said first channel,and when in said open position forms a diverging passage from said pivotaxis to said fixed outer wall.
 5. The integrated air duct of claim 1wherein said opening and said first channel each have transverse crosssections that are substantially circular.
 6. The integrated air duct ofclaim 5 wherein said second channel fully encircles said first channel.7. The integrated air duct of claim 5 wherein said first channel issubstantially coaxial with said opening.
 8. The integrated air duct ofclaim 5 wherein said first channel is axially offset relative to saidsecond channel.
 9. The integrated air duct of claim 5 comprising aplurality of said movable panels distributed along the circumference ofsaid first channel.
 10. The integrated air duct of claim 5 comprising aplurality of said movable panels distributed along the circumference ofsaid first channels, said movable panels alternating with an equalnumber of struts joining said fixed inner wall to said fixed outer wall,each said strut having a fuel injector mounted thereto.
 11. Theintegrated air duct of claim 1 wherein said movable panel is defined asa flow-diverting panel and said integrated air duct further comprises anadditional movable panel defined as a diffuser panel, mounted withinsaid fixed outer wall downstream of said flow diverting panel, saidflow-diverting and diffuser panels each having a pivotally mounted endand a free end, said flow-diverting and diffuser panels meeting at saidfree ends.
 12. The integrated air duct of claim 1 wherein said movablepanel is defined as a flow-diverting panel and said integrated air ductfurther comprises a downstream movable panel mounted to said fixed outerwall downstream of said flow diverting panel, said flow-diverting anddownstream panels when open providing a through-passage through saidsecond channel and when closed forming an enclosed chamber in saidsecond channel.
 13. The integrated air duct of claim 1 in which saidmovable panel is one of a first plurality of movable panels each mountedwithin said fixed outer wall at a pivot axis upstream of said leadingrim of said first channel for pivoting between an open position allowingincoming air to enter both said first and second channels and a closedposition obstructing air entry into said second channel and therebycausing substantially all incoming air to enter said first channel, saidintegrated air duct further comprising a second plurality of movablepanels mounted to said fixed outer wall downstream of said firstplurality, each of said first and second pluralities of movable panelswhen open providing a through-passage through said second channel andwhen closed forming an enclosed chamber in said second channel.
 14. Theintegrated air duct of claim 1 in which said movable panel is one of afirst plurality of movable panels each mounted within said fixed outerwall at a pivot axis upstream of said leading rim of said first channelfor pivoting between an open position allowing incoming air to enterboth said first and second channels and a closed position obstructingair entry into said second channel and thereby causing substantially allincoming air to enter said first channel, said integrated air ductfurther comprising a second plurality of movable panels mounted to saidfixed outer wall downstream of said first plurality, said first andsecond pluralities of movable panels arranged to be movable to aposition providing said second channel with a convergent/divergentprofile to decelerate incoming supersonic flow first to substantiallysonic flow and then to subsonic flow.
 15. The integrated air duct ofclaim 1 wherein said means for moving said movable panel is anelectromagnetic actuator.
 16. An aircraft engine having multiplepropulsion systems, said aircraft engine comprising: a ramjet, a boosterpropulsion system, and an integrated air duct comprising: a fixed outerwall with an opening for incoming air, wherein said opening has aforward-extending upper lip and a rearward-extending downstream end, afixed inner wall dividing said duct into (i) a first channel extendingfrom a leading rim downstream of said opening to said ramjet and (ii) asecond channel between said fixed inner wall and said fixed outer wallleading to said booster propulsion system, a movable panel mountedwithin said fixed outer wall at a pivot axis downstream of said upperlip and approximately coplanar with or slightly forward of saiddownstream end, said pivot axis also being upstream of said leading rimof said first channel for pivoting between an open position allowingincoming air entering through said opening to enter said first andsecond channels simultaneously and a closed position obstructing airentry into said second channel and thereby causing substantially allincoming air entering through said opening to enter said first channel,and means for moving said movable panel between said open position andsaid closed position.
 17. The aircraft engine of claim 16 wherein saidbooster propulsion system is a turbojet.
 18. The aircraft engine ofclaim 16 wherein said booster propulsion system is a rocket motor. 19.The aircraft engine of claim 16 wherein said booster propulsion systemis a combination turbojet and rocket motor.
 20. The aircraft engine ofclaim 16 wherein said ramjet is a scramjet and said engine furthercomprises rocket motors positioned within said first channel tosupplement said scramjet.
 21. The aircraft engine of claim 16 whereinsaid first channel is of substantially circular cross section and saidmovable panel is one of a plurality of movable panels mounted withinsaid fixed outer wall at a pivot axis upstream of said leading rim ofsaid first channel for pivoting between an open position allowingincoming air entering through said opening to enter both said first andsecond channels and a closed position causing substantially all incomingair entering through said opening to enter said first channel, saidmovable panels when in said closed position forming a converging flowpassage toward said first channel.
 22. The aircraft engine of claim 21wherein said first channel is of substantially circular transverse crosssection and said second channel fully encircles said first channel, saidmovable panels distributed around said first channel.
 23. The aircraftengine of claim 21 wherein said first channel is of substantiallycircular transverse cross section and is axially offset relative to saidsecond channel.